Sen. Flake visits John McCain at his Arizona cabin: 'He's working hard and gaining strength'

4 August 2015: United States Senators from Arizona, Jeff Flake (L) and John McCain (R) attend the game between the Arizona Diamondbacks and the Washington Nationals at Nationals Park in Washington, D.C.

McCain, 81, was diagnosed with glioblastoma over the summer, and in July, he began chemotherapy and radiation treatment at the Mayo Clinic in Phoenix. In December, he was hospitalized at Walter Reed National Military Medical Center in Bethesda, Maryland. He subsequently returned to Arizona, and has been there since.

Senator John McCain poses for a photo with his daughter Meghan on ABC's "The View," Oct 23, 2017.

Astrid Stawiarz/Getty Images

NEW YORK, NY - FEBRUARY 05: Meghan McCain visits the SiriusXM Studios on February 5, 2018 in New York City.

Also on Saturday, CNN aired an interview with McCain's daughter, "The View" co-host Meghan McCain, who also provided an update on her father's health.

"He's doing really good, all things considered," she said. "I've been very open. He had sort of a bad bout at Christmas time. He was hospitalized at Walter Reed. He had ramifications from his chemotherapy. He had pneumonia. But he's made this, like, really incredible comeback. And I was with him at Christmas time. And he's doing a lot of physical therapy ... He's doing good."